1. Field of the Invention
The present invention relates to an object, a method, or a manufacturing method. In addition, the present invention relates to a process, a machine, manufacture, or a composition of matter. In particular, the present invention relates to, for example, a semiconductor layer, a semiconductor device, a display device, a liquid crystal display device, or a light-emitting device. In addition, the present invention relates to a method for manufacturing a semiconductor device, a display device, a liquid crystal display device, or a light-emitting device. Alternatively, the present invention relates to a driving method of a semiconductor device, a display device, a liquid crystal display device, or a light-emitting device. In particular, the present invention relates to a semiconductor device, a display device, or a light-emitting device each including a transistor, or a driving method thereof, for example. Further, the present invention relates to, for example, an electronic device including the semiconductor device, the display device, or the light-emitting device.
Note that in this specification, a semiconductor device refers to any device that can function by utilizing semiconductor characteristics, and an electro-optical device, a semiconductor circuit, an electronic device, and the like are all included in the category of the semiconductor device.
2. Description of the Related Art
A technique for forming a transistor by using a semiconductor layer formed over a substrate having an insulating surface has attracted attention. The transistor is applied to a wide range of semiconductor devices such as an integrated circuit and a display device. A silicon layer is known as a semiconductor layer applicable to a transistor.
Whether an amorphous silicon layer or a polycrystalline silicon layer is used as a semiconductor layer in a transistor depends on the purpose. For example, in the case of a transistor included in a large display device, an amorphous silicon layer, which can be formed using an established technique for forming a film over a large substrate, is preferably used. On the other hand, in the case of a transistor included in a high-performance display device where driver circuits are formed over the same substrate, a polycrystalline silicon layer, which can form a transistor having a high field-effect mobility, is preferably used. As a method for forming a polycrystalline silicon layer, high-temperature heat treatment or laser light treatment which is performed on an amorphous silicon layer has been known.
In recent years, an oxide semiconductor layer has attracted attention. For example, a transistor which includes an amorphous oxide semiconductor layer containing indium, gallium, and zinc has been disclosed (see Patent Document 1). Further, a transistor including three amorphous oxide semiconductor layers which are stacked has been disclosed (see Patent Document 2 and Patent Document 3).
An oxide semiconductor layer can be formed by a sputtering method or the like, and thus can be used for a channel formation region of a transistor in a large display device. A transistor including an oxide semiconductor layer has a high field-effect mobility; therefore, a high-performance display device where driver circuits are formed over the same substrate can be formed. Moreover, there is an advantage that capital investment can be reduced because part of production equipment for a transistor including an amorphous silicon layer can be improved to be used for an oxide semiconductor layer.
Note that homologous compounds represented by InMO3(ZnO)m (M is Fe, Ga, or Al and m is a natural number) are known (see Non-Patent Document 1). Among homologous compounds represented by InMO3(ZnO)m, a crystal where M is gallium (Ga) is sometimes referred to as “Kumizuka crystal” named after Dr. Noboru Kimizuka who succeeded in synthesizing the crystal for the first time.